A serial printer is known as one type of printers having a head pin. The serial printer prints with the head pin kept in contact with a paper sheet. The serial printer prints with the printhead placed at a specific printing position while the printhead performs a first scan on the printing medium. Techniques of controlling damage on the head pin, such as breaking of the head pin, during printing or during scanning is known in the field of the serial printer. One of the techniques of controlling the damage of the head pin includes detecting both edges of a paper sheet when the paper sheet is fed, and causing the printhead not to print outside the paper sheet.
According to another technique, an optimum gap is set by controlling a carriage as a driver of a printing mechanism and a paper guide driving motor in response to a paper width detected by an optical paper-thickness detector.
According to yet another technique, when the printhead is in a print disabled area close to an edge of paper, print data corresponding to the area is discarded, and paper transportation only is performed with the scanning of the printhead suspended.
The above-described techniques are disclosed in Japanese Unexamined Utility Model Application Publication No. 05-028650 and Japanese Laid-open Patent Publication No. 08-207381.
According to another technique, a change in the color of the paper and platen is detected, and the change of the color is thus determined as the edge of the paper. However, if a ruler line is pre-printed on the paper itself, the change in the color within the paper may be erratically recognized as the edge of the paper. If the change is erratically recognized as the edge of the paper, printing is not performed even within a printable area of the paper. Printing is desirably performed on a printing area with such an erratic recognition controlled. To this end, a user may turn off a paper-width detection sensor while printing.
When printing is performed on a paper sheet having a width smaller than a printable range with the sensor switched off, the edge of the paper sheet is not detected. The head pin may be caught and damaged on the edge of the paper. The head pin may be caught and damaged by other irregularities, such as a step in the thickness of a plurality of stacked paper sheets and a punch hole formed in the paper sheet. In the printing process of the serial printer, the printhead slides as the head pin, after being driven toward the paper, is retracted to the printhead. If the head pin is driven to an area such as a punch hole other than the paper, the printhead starts to move before the head pin is fully retracted in the printhead. The head pin may thus be caught on the paper.